Tailoring Oxygen-Bridged Ru─Ti Asymmetric Pairs Enables Low-Overpotential Two-Electron Water Oxidation.

Electrochemical two-electron water oxidation (2e-WOR) offers a promising direct route to on-site hydrogen peroxide (H2O2) production, yet state-of-the-art catalysts still suffer from intrinsically low selectivity and large overpotentials, especially in near-neutral media. Equally unresolved is how the electrolyte composition steers the competition between 2e-WOR and the thermodynamically favored four-electron oxygen evolution reaction (OER). Here we employed a monolayer TiO2 nanosheet platform to anchor atomically dispersed 3d/4d transition-metal centers (Ru1, Cu1, Co1, and Fe1). Among them, Ru1-TiO2 delivers an optimal Faradaic efficiency (FE) of 60.8% at a low overpotential of 130 mV. Further analysis reveals that the oxygen-bridged Ru─Ti (Ru─O─Ti) asymmetric dimer establishes a gradient d-p-d orbital coupling. This electronic motif strengthens the adsorption of HCO3* while attenuating the over-binding of OH*, thereby switching the surface termination from OH* to HCO3*-rich. Consequently, a bicarbonate-mediated 2e-WOR pathway is selectively activated over the Ru─O─Ti sites, which is much more favorable than the conventional OH*-OH* coupling route. These findings underscore that gradient orbital coupling across asymmetric atomic pairs act as an electronic lever to redirect the catalytic trajectory, furnishing a general principle for pathway control in diverse electrosynthesis systems.